In receivers for television, and monitor displays for personal computers, it has been traditional to use either a CRT (cathode ray tube) set or a LCD (liquid crystal display).
A CRT is made up of an electron gun, a deflector for sweeping an electron beam projected from the electron gun and a fluorescent screen that illuminates when it has an electron beam impinging thereon. The electron gun is formed, e.g., of a filament made of a resistor such as a tungsten wire, and a focusing coil for focusing thermoelectrons emitted from the filament.
Designed to heat the filament by passing electric current through it to emit thermoelectrons, an electron gun of this type is poor in energy efficiency for extracting the electrons into a required beam, since a portion of the electric energy is consumed to emit light and heat. Such electron guns are also deficient in safety, because they entail a high voltage and an elevated temperature.
An electron gun of field emission type is also available in which a high voltage is applied to a pointed metal or semiconductor and an electron beam is extracted using an electric field concentrated at this pointed end. Energy efficiency is poor here, too, because of the need for a high voltage.
Because the deflector deflect the direction of travel of an electron beam by an electromagnetic force, it must be capable of attaining greater angles of deflection for corresponding to a large fluorescent surface, namely the screen, so it is necessary that the deflector has a large volume in size or applied in a big electrical power.
Thus, the electron guns in the CRT system are as poor in energy efficiency as 0.01% (in quantum efficiency as 0.1%), and are hence unsuitable for a power saving apparatus. Further, in the principles of their operation they can not be made thin, and hence it is impossible for them to be made flat such as for a wall type television.
In order to solve the problems of the CRT system, the LCD device has come to spread widely. The LCD device, however, has left the problems mentioned below.
The LCD device is made up of a backlight panel as a light source, a liquid crystal and a polarizer interposed between substrates which have electrodes for controlling the light transmittance of each of the pixels, a color filter, and a drive circuit for applying voltages to the electrode.
In any LCD device of this type, the attempt to raise its brightness requires raising the brightness of the backlight panel light source, but this entails raising the brightness of pixels that are not required to raise its brightness. Hence, poor energy efficiency ensues here. Further, the backlight panel light source, which is made up of fluorescent tubes or a LED array panel or an EL panel, is hard in the principles of its operation to obtain as high a brightness as in the CRT system.
Also, in recent years there has been proposed an image display system which by using an electron gun for each of the pixels can be made as thin as the LED system and provides a brightness as high as with the CRT system. The electron gun in this system is an electron gun of field emission type having a pointed area for each pixels, and the display is constituted by these pixels which are formed on, e.g., the surface of a semiconductor substrate by machining the semiconductor surface. In such a system, it is technologically difficult to machine so that a pointed area may be formed for each of the pixels, and there is also the problem that even if being effective the electric field concentration of the pointed area, even high voltage is needed in order to extract electrons from the semiconductor. For these reasons, the system has not yet been put to practical use.
In sum, the conventional image displays as mentioned above leave the problems unsolved that they are poor in energy efficiency, incapable of being made thin and much unsatisfactory in brightness.
With those problems taken into account, it is an object of the present invention to provide an electron gun of quantum size effect type which by using a quantum size effect makes it possible to extract electrons easily from a semiconductor and can be allocable as each of pixels.
It is another object of the present invention to provide an image display apparatus using such electron guns that is high in quantum efficiency, high in brightness and small in thickness.
It is a further object of the present invention to provide methods of making an electron gun of quantum size effect type and an image display apparatus as mentioned above.